1. Field of the Invention
The present invention relates to X-Y tables of the type employed in the semiconductor industry to accurately position a wafer or a semiconductor device relative to a stationary tool or station.
More particularly, the present invention relates to apparatus and a method for improving the accuracy of positioning an X-Y table and for eliminating repeatable type accuracy errors.
2. Description of the Prior Art
Heretofore, X-Y tables have been employed in the semiconductor industry to position wafers while making semiconductor devices and for positioning semiconductor devices or tools during bonding and packaging processes. The most common type of X-Y table employs highly accurate sliders and stages similar to those set forth in Kulicke and Soffa Industries U.S. Pat. No. 3,046,006. The stages or slides of the X-Y table may be driven by linear motors, voice coil motors or conventional servo motors acting through accurate leads screws or other means.
It is generally recognized that prior art X-Y tables have errors or imperfections which affect the proper positioning of the top stage of an X-Y table which supports either the tool or the device to be processed. For example: (1) The slider castings may be imperfect or not square. (2) The lead screw is not accurate. (3) The lead screw and motor shaft are not axially aligned causing an off-axis sinusoidal error. (4) The sliders are warped or damaged. (5) The gibbs are warped or damaged. (6) The way bar which is employed with some X-Y tables is not rigid and flexes under high forces. The aforementioned errors are repeatable and may be detected with sophisticated test equipment such as a laser interferometer.
Prior art machine tools such as numerical controlled machine tools require high accuracy and have been calibrated at the factory where made. The errors which occur as a result of positioning a table with a long lead screw do not change in the field. This positioning error information has been incorporated into the electronic controls of the numerical control machine tools so that the X or Y linear position of the lead screw is corrected or compensated to accurately position the working platform or table of the machine tool. However, this prior art error correction method does not correct for X or Y deviations which occur as a result of the orthogonal movement.
It would be desirable to provide a simplified procedure and apparatus for detecting the X-Y table repeatable errors of semiconductor processing machines which change in the field. Further it would be desirable to provide error compensation which will only be limited by the positioning apparatus without having to provide more accurate and more expensive X-Y tables.